The present invention is related generally to power train systems in wind turbines, and specifically, to an improved modular wind turbine power train system consisting of a compound split planetary gearing system incorporating a closed carrier flex pin system in a high torque stage and an open carrier flex pin system in a low torque stage, coupled to a generator in a modular assembly mounted on a common support structure.
Wind turbine designers are developing new and improved system architectures that are aimed at producing lean and reliable machines. One solution being pursued is a hybrid wind turbine which is a combination of a simplified power train (commonly a single-stage planetary gearing system) and a mid-speed generator. To make this configuration as lean as possible, if a higher step up ratio in the planetary gearing system is applied, a reduced size, faster running generator can also be applied. In other words, if the wind turbine rotates at a given speed of “a” revolutions per minute (rpm), and if the planetary gearing system step up ratio is “b”, the generator will rotate at a speed of (a×b). The higher the step up ratio “b” is, the faster the generator will rotate. As a general rule, a smaller generator that rotates faster will be lighter in mass and lower in cost, thus leading to a leaner system design. Therefore, there is an industry need to increase the step up ratio “b” within as small a space as possible, and with as small a mass as possible.
Depending upon the speed radio desired, the power train can be configured as either a planetary system, a star system, or a combination thereof. A planetary gearing system is normally comprised of a sun gear in the center, orbiting planet gears (usually but not always three in number) in mesh with the sun gear, a rotating planetary carrier (coaxial with the sun gear) which is a structural member that holds the planet gears in a fixed relative position, and a ring gear which is also coaxial with the sun gear that surrounds and meshes with all the orbiting planet gears. Input and output shafts extend from the sun gear and carrier respectively. In operation, the input shaft rotatably drives the sun gear, compelling each planet gear to rotate about its own axis and, because the ring gear is mechanically grounded, causing the planet gears to orbit the sun gear. the planet gear orbital motion turns the planet carrier, and hence the output shaft in the same direction as the input shaft. Traditionally, each of the planet gears is supported by one or more rows of planetary bearings which are supported on a non-rotating, but orbiting, pin that is fixed at each end to a closed planetary carrier. This arrangement theoretically splits the input torque along a number of equal load paths corresponding to the number of planet gears, and in so doing, reduces the magnitude of the gear forces acting at each gear mesh to a correspondingly smaller number.
An alternative configuration is a star system, which is similar to the planetary system except that the planet carrier is mechanically grounded and the ring gear is rotatable, with the output shaft extending from the ring gear. Because the planet carrier is grounded, the planet gears cannot orbit the sun and therefore are referred to as star gears. In operation, the input shaft drive the sun gear, compelling each star gear to rotate about its own axis. The rotary motion of the star gears turns the ring gear, and hence the output shaft, in a direction opposite that of the input shaft.
Gears in a planetary gearing system are normally designed as spur, helical, or a double helical varieties. Regardless of which gear design is used, there are two commonly observed drawbacks. The first is that machining tolerances necessarily create variation in clearances among all the gear meshes. This means that as torsion is applied into the gearing system, the gear mesh with least clearance will initially begin supporting the load by itself, until this gear mesh deflects enough so that the gear mesh with the next least clearance begins supporting the load. This phenomenon will progress until all the entire load is fully supported by some number of the gear meshes. In other words, some gear meshes will support more load than others. There are means for introducing flexibility into the gear meshes to restore equalization of loads in the gear meshes, one being use of a floating sun gear in a three planet system.
The second drawback to a conventional planetary gearing system which employs a closed planetary carrier having two walls connected by webbing is that applied torsion will twist the carrier, advancing one end of the planetary pin rotationally about the axis of the carrier ahead of the other end. This advancement misaligns the planetary gears with the mating sun gear and ring gear. The planetary gear bearings will also be subjected to this same amount of misalignment.
Generally, the output shaft of the planetary gearing system in a wind turbine is coupled directly to the generator, allowing rotation of the wind turbine blades to drive the generator through the planetary gearing system. To achieve this direct coupling, generators have been either supported directly on the output shaft, such as shown in WO 2009-100720 A2 to Innovative Windpower AG, or have been supported directly on the grounded housing of the planetary gearing system. The primary disadvantage of these configurations is apparent when servicing either the planetary gearing system or the generator, as due to the integral coupling and assembly thereof, both components must be removed together to enable the servicing of either unit. Furthermore, to access the main shaft of the planetary gearing system which is supporting and/or driving the generator, the nose cone and turbine rotor assembly must be removed from the wind turbine to gain access to the upwind end of the drive
Accordingly, it would be advantageous to provide a geared power train for use in a wind turbine application which is configured to maximize the step-up ratio “b” within a limited space, allowing for lighter mass generators and lower overall system costs, and which has a modular assembly, allowing for servicing and/or removal of either the generator or the planetary gearing system without requiring disassembly of the remaining components.